| Message ID | 158823802979.28101.9340462887738957616.stgit@pasha-ThinkPad-X280 |
|---|---|
| State | New |
| Headers | show |
| Series | replay: implement fair mutex | expand |
On 30/04/20 11:13, Pavel Dovgalyuk wrote: > In record/replay icount mode main loop thread and vCPU thread > do not perform simultaneously. They take replay mutex to synchronize > the actions. Sometimes vCPU thread waits for locking the mutex for > very long time, because main loop releases the mutex and takes it > back again. Standard qemu mutex do not provide the ordering > capabilities. > > This patch adds a "queue" for replay mutex. Therefore thread ordering > becomes more "fair". Threads are executed in the same order as > they are trying to take the mutex. > > Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru> > --- > replay/replay-internal.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/replay/replay-internal.c b/replay/replay-internal.c > index eba8246aae..2e8a3e947a 100644 > --- a/replay/replay-internal.c > +++ b/replay/replay-internal.c > @@ -22,6 +22,9 @@ > It also protects replay events queue which stores events to be > written or read to the log. */ > static QemuMutex lock; > +/* Condition and queue for fair ordering of mutex lock requests. */ > +static QemuCond mutex_cond; > +static unsigned long mutex_head, mutex_tail; > > /* File for replay writing */ > static bool write_error; > @@ -197,9 +200,10 @@ static __thread bool replay_locked; > void replay_mutex_init(void) > { > qemu_mutex_init(&lock); > + qemu_cond_init(&mutex_cond); > /* Hold the mutex while we start-up */ > - qemu_mutex_lock(&lock); > replay_locked = true; > + ++mutex_tail; > } > > bool replay_mutex_locked(void) > @@ -211,10 +215,16 @@ bool replay_mutex_locked(void) > void replay_mutex_lock(void) > { > if (replay_mode != REPLAY_MODE_NONE) { > + unsigned long id; > g_assert(!qemu_mutex_iothread_locked()); > g_assert(!replay_mutex_locked()); > qemu_mutex_lock(&lock); > + id = mutex_tail++; > + while (id != mutex_head) { > + qemu_cond_wait(&mutex_cond, &lock); > + } > replay_locked = true; > + qemu_mutex_unlock(&lock); > } > } > > @@ -222,7 +232,10 @@ void replay_mutex_unlock(void) > { > if (replay_mode != REPLAY_MODE_NONE) { > g_assert(replay_mutex_locked()); > + qemu_mutex_lock(&lock); > + ++mutex_head; > replay_locked = false; > + qemu_cond_broadcast(&mutex_cond); > qemu_mutex_unlock(&lock); > } > } > Queued, thanks. Paolo
diff --git a/replay/replay-internal.c b/replay/replay-internal.c index eba8246aae..2e8a3e947a 100644 --- a/replay/replay-internal.c +++ b/replay/replay-internal.c @@ -22,6 +22,9 @@ It also protects replay events queue which stores events to be written or read to the log. */ static QemuMutex lock; +/* Condition and queue for fair ordering of mutex lock requests. */ +static QemuCond mutex_cond; +static unsigned long mutex_head, mutex_tail; /* File for replay writing */ static bool write_error; @@ -197,9 +200,10 @@ static __thread bool replay_locked; void replay_mutex_init(void) { qemu_mutex_init(&lock); + qemu_cond_init(&mutex_cond); /* Hold the mutex while we start-up */ - qemu_mutex_lock(&lock); replay_locked = true; + ++mutex_tail; } bool replay_mutex_locked(void) @@ -211,10 +215,16 @@ bool replay_mutex_locked(void) void replay_mutex_lock(void) { if (replay_mode != REPLAY_MODE_NONE) { + unsigned long id; g_assert(!qemu_mutex_iothread_locked()); g_assert(!replay_mutex_locked()); qemu_mutex_lock(&lock); + id = mutex_tail++; + while (id != mutex_head) { + qemu_cond_wait(&mutex_cond, &lock); + } replay_locked = true; + qemu_mutex_unlock(&lock); } } @@ -222,7 +232,10 @@ void replay_mutex_unlock(void) { if (replay_mode != REPLAY_MODE_NONE) { g_assert(replay_mutex_locked()); + qemu_mutex_lock(&lock); + ++mutex_head; replay_locked = false; + qemu_cond_broadcast(&mutex_cond); qemu_mutex_unlock(&lock); } }
In record/replay icount mode main loop thread and vCPU thread do not perform simultaneously. They take replay mutex to synchronize the actions. Sometimes vCPU thread waits for locking the mutex for very long time, because main loop releases the mutex and takes it back again. Standard qemu mutex do not provide the ordering capabilities. This patch adds a "queue" for replay mutex. Therefore thread ordering becomes more "fair". Threads are executed in the same order as they are trying to take the mutex. Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru> --- replay/replay-internal.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)